Circuit for signalling the operation of a circuit protecting device

ABSTRACT

A circuit for indicating the operative state of a circuit breaker which protects a load from an alternating voltage source, wherein a lamp is coupled to said source to light when the breaker is open, but is prevented from lighting when the breaker is closed by a forward biased diode which limits the voltage across the lamp.

I United States Patent 51 3,662,369

Vinsani et al. 1 May 9, 1972 [54] CIRCUIT FOR SIGNALLING THE OPERATION OF A CIRCUIT References Cited PROTECTING DEVICE UNlTED STATES PATENTS [72] Invemms Mari vinsani Milan; Trim, 3,423,745 1/1969 Williams ..340/176 Bregnano, both of Italy [73] Assignee: Honeywell Information Systems Italia y Caldwell S.P.A., Milan, ltaly Assistant E.\aminerDaniel Myer Almrne vGeorge V. Eltgroth, Lewis P. Elbinger and Frank L. 22 Filed: Feb. 5, 1970 Neuhauser [2]] Appl. No.: 8,952

[57] ABSTRACT [30] Foreign Application P i it D m A circuit for indicating the operative state of a circuit breaker which protects a load from an alternating voltage source. Feb. 5, 1969 ltaly ..12445 A/69 wherein a lamp is Coupled to Said Source to light when the breaker is open, but is prevented from lighting when the [52] US. Cl. ..340/250, 200/167 A, 340/253 B breaker is closed by a f d biased diode which limits the [51 Int. Cl. ..G08b 2-1/00 voltage across the lamp [58] Field of Search ..340/250, 176, 253 B; 315/120,

315/129-136; 324/51, H0, I33; 337/]; 200/167 A 2 Claims, 4 Drawing Figures PATENTEMY 91912 3,662,369

FIG.1

FIG. 3 FIG. L

Mar/'0 VIN SAN! CeL/o TRINCA INVENTORS ATTORNEY CIRCUIT FOR SIGNALLING THE OPERATION OF A CIRCUIT PROTECTING DEVICE BACKGROUND OF THE INVENTION The present invention relates to a simple circuit for signaling the operation of a circuit protecting device.

Circuit protecting devices which operate to isolate either a whole apparatus or part thereof are known in the art, particularly in the fields of electricity and electronics. The isolating operation takes place as soon as an unusual operating condition, dangerous or prejudicial to the apparatus, such as overheating, overloading or excessive voltage, occurs. A wellknown particularly simple and economical device which is effective against overloads is the common fuse.

Also known is the fact that when a plurality of fuses is employed to protect different sections of the same apparatus, a diagnostic function is provided by the fuses in addition to their basic protective function. The diagnostic function is provided because the bum-out of one or more fuses provides an indication effective in delimiting the portion of the apparatus in which the overload has occurred and in facilitating the identification of the causes and malfunctions which caused the fuses to burn out.

To render this diagnostic function more useful and practical, there must be easy identification of the burned-out fuses among the set of protecting fuses. However, easy identification of the burned-out fuses is not always possible because the fuses are usually contained in enclosures and, thus, are not directly accessible, and because the wires of the fuses are often so thin that it is difficult to determine the integrity of a fuse by visual inspection. Special fuses are known in which a visible color change occurs in certain parts of their supporting structure when the fuse burns out. Nevertheless, visual inspection is necessary and the latter type of fuse must, therefore, be arranged in easily accessible enclosures provided with windows.

In addition to the difficulty of establishing the diagnostic function by visual inspection of a set of fuses, a signaling means requiring such a visual inspection is not of the same quality as that of other devices more commonly employed for checking and controlling the operation of the apparatus, the operation of which is generally signaled by the lighting of lamps.

To alleviate these disadvantages, it has been proposed to connect a signal lamp in parallel with each fuse, wherein when the fuse is intact, no voltage is applied across the lamp terminals, but when the fuse is burned out a significant fraction of the supply voltage, depending on the relative resistance of the lamp and the load supplied through the fuse, is applied to the lamp.

However, this latter arrangement has the considerable disadvantage of requiring the use of lamps of different resistances, each one depending on the value of the load with which it must operate, whereas, from the point of view of standardization it is preferable to use electrical components of the same type.

An additional disadvantage of the last described arrangement is that because the load may vary and reach extreme values under the anomalous conditions which cause the operation of the protecting device, a lamp in parallel with a burnedout fuse frequently operates under unfavorable conditions, resulting either in a low level of brightness provided by the lamp or in the burning out of the lamp, itself, due to an excessive overload.

An additional disadvantage of the last-described arrangement is that both the load and the protecting device are influenced by the current flowing through the lamp, however small such current may be. Such current cannot be tolerated in many cases because it may cause irreparable damage to the apparatus, whereas the object of the protecting device is to prevent such damage.

Therefore, the object of the present invention is to provide signaling means which are not subject to the above-mentioned disadvantages and which may be used with any apparatus or portions thereof.

The signaling means of the instant invention is characterized by its extreme simplicity and low cost and by its capability for employment with every type of protecting device which operates by interrupting an AC supply circuit. Such signalling means provides an optical indication of the operation of the protecting device, wherein the indicating lamp is not physically associated with the protecting device itself but may be located at any convenient place in the apparatus. Finally, the resistance of the indicating lamp is independent of the value of the protected load.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described with reference to the accompanying drawing, wherein:

FIG. 1 is a schematic diagram of a signaling circuit in accordance with the invention for use with apparatus supplied from a positive voltage source;

FIG. 2 is a schematic diagram of a signaling circuit in accordance with the invention for use with apparatus supplied from a negative voltage source;

FIG. 3 is a schematic diagram of a signaling circuit in accordance with the invention and supplied by an auxiliary voltage source; and

FIG. 4 is a schematic diagram of an alternative form of the signaling circuit of the invention, adapted for apparatus supplied by an alternating voltage source.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a DC voltage source G supplies a suitable positive voltage V to a load C through a protecting fuse F. A lamp L and a resistor R of suitable value are connected in series between the high voltage terminal of fuse F and a ground reference voltage. Thus, the series combination of lamp L and resistor R are connected in parallel with load C.

The connection point between resistor R and lamp L is coupled through a diode D to the low voltage terminal of fuse F. Diode D is connected so as to be forward biased by the voltage +V and, therefore, to conduct when the fuse is intact. With the fuse in this closed condition, a current having a value of approximately V/R flows through diode D and resistor R. Lamp L, being shunted by conducting diode D, does not light because across its terminals is only the voltage drop of diode D. This voltage drop is very small, for a silicon diode being about 0.7 v. and for a germanian diode being only about 0.3 v.

If fuse F burns out, the low voltage terminal of the fuse drops to 0 V., or ground potential. Diode D thereupon becomes reverse biased in the path comprising lamp L, diode D, and load C and does not conduct. With the fuse in this open condition, the voltage +V causes a substantial current to flow through lamp L and resistor R to ground. If R, represents the resistance of lamp L and R represents the resistance of resistor R, the value of this current is:

/RL R) It is possible to choose the most suitable values of R and R relative to the value of voltage +V, so as to operate lamp L at the best working brightness.

The operation of the signaling circuit is completely independent of load C. Moreover, when the fuse is burned out, load C receives no current, with the exception of the negligible inverse current through diode D.

A substantially identical circuit is used in the case where the DC voltage source is negative. In this circuit, FIG. 2, the arrangement of the components is the same as that of the embodiment of FIG. 1, only the direction of conduction of diode D being inverted.

The embodiments of FIGS. 1 and 2 were shown for use with a load having one terminal connected to ground, a custom normally followed for reasons of safety. However it is apparent that these same signaling and protecting circuits of the invention may be used also with loads which are not grounded (floating-voltage circuits). Moreover, difierent signaling devices, such as neon-lamps (if the applied voltage is more than 70 v.), buzzers, etc., may be employed. Germanium or silicon diodes or other semiconductor components may be used in the circuit. Furthermore, a thermal relay or any other type of circuit breaker may be substituted for the fuse.

FIG. 3 shows another embodiment wherein the arrangement of the components relative to the load and to the supply voltage is the same. However, the signaling circuit is coupled to a voltage source V which is diflerent from the supply volta e V.

In order that, under normal operating conditions, diode D be forward biased and, therefore, conducting so as to cause a substantially null voltage to be applied to lamp L, it is necessary that V V (I If the polarity of the diode is inverted from that shown in FIG. 3, connection (1) is, instead When the .fuse is burned out, in order to have diode D reverse biased so as to isolate load C, it is necessary that the voltage present at point 1 be positive.

If (1 represents the ratio of the voltage drop across lamp L to the full voltage applied to the series-connected lamp L and resistor R, then a (R /R R) where R represents the resistance of lamp L. Therefore, for point 1 to be positive,

Va(VV') O (2) Conversely, if the polarity of the diode is inverted from that shown in FIG. 3, the corresponding requirement is V- a (V V) Conditions (I) and (2) demonstrate that if V is positive, V may be negative within the limits defined by condition (2). Thus, both V and V may vary in time, provided that at every instant the specified conditions are satisfied.

However, voltage V cannot be alternating, because for negativevalues of V, and consequently of V, condition (2) cannot be satisfied.

FIG. 4 illustrates a variation of the circuit of FIG. 3 which overcomes this limitation. A diode D is serially connected to lamp L, and has the same direction of conduction relative to point 1 as diode D,.

In this circuit, if the fuse is intact, condition (1), above, which requires that V be greater than V, need not be satisfied. If V is greater than V, lamp L is efi'ectively shunted by diode D,, but if V is less than V, both diodes D, and D, are reverse biased and the lamp is prevented from lighting.

1. For use with an electrical circuit wherein a source of alternating voltage provides current through a feeding line to a load, and wherein a protecting circuit breaking device is adapted to break the continuity of said feeding line, a circuit for signalling the operation of said circuit breaking device I comprising: si nailing means a first dio e, connected in a series circuit with said signalling means,

a resistor connected in series with a first terminal of said series circuit,

said series circuit being connected to a second terminal to a point on said feeding line immediately upstream of said circuit breaking device,

a reference voltage coupled to said resistor, and

a second diode connected between a point on said feeding line immediately downstream of said circuit breaking device and said first terminal, said first and second diodes have the same directions of conduction relative to said feeding line.

2. For use with a circuit wherein a two-terminal circuit breaking device transmits current from a first circuit point having a first alternating voltage value to a load, a first terminal of said device being connected to said first circuit point and a second terminal of said device being connected to said load, an indicating circuit for representing the state of said circuit breaking device comprising:

an indicating member,

a first nonlinear device connected in a series circuit with said indicating member, said series circuit being connected to said first circuit point,

a second circuit point having a second voltage value,

a resistor connected between said second circuit point and said series circuit, and

a second nonlinear device connected between said resistor and said second terminal, said first and said second nonlinear devices connected to be conducting in a path from said first and second terminals to said second circuit point. 

1. For use with an electrical circuit wherein a source of alternating voltage provides current through a feeding line to a load, and wherein a protecting circuit breaking device is adapted to break the continuity of said feeding line, a circuit for signalling the operation of said circuit breaking device comprising: signalling means, a first diode, connected in a series circuit with said signalling means, a resistor connected in series with a first terminal of said series circuit, said series circuit being connected to a second terminal to a point on said feeding line immediately upstream of said circuit breaking device, a reference voltage coupled to said resistor, and a second diode connected between a point on said feeding line immediately downstream of said circuit breaking device and said first terminal, said first and second diodes have the same directions of conduction relative to said feeding line.
 2. For use with a circuit wherein a two-terminal circuit breaking device transmits current from a first circuit point having a first alternating voltage value to a load, a first terminal of said device being connected to said first circuit point and a second terminal of said device being connected to said load, an indicating circuit for representing the state of said circuit breaking device comprising: an indicating member, a first nonlinear device connected in a series circuit with said indicating member, said series circuit being connected to said first circuit point, a second circuit point having a second voltage value, a resistor connected between said second circuit point and said series circuit, and a second nonlinear device connected between said resistor and said second terminal, said first and said second nonlinear devices connected to be conducting in a path from said first and second terminals to said second circuit point. 